How to change the first day of a week in calendar?

Usually, the first day of a week in calendar is Sunday, but you can change it as following.

• Please click Options in Tools menu, and then click Calendar on the left side of this interface. After that, you change it in the drop-down menu of First day of a week.
  

This article is suitable for EfficientPIM, Efficient Man's/Lady's Organizer, Efficient Reminder, and Efficient Calendar.